(i) Technical Field
The present invention relates to semiconductor devices and methods for fabricating semiconductor devices.
(ii) Related Art
Semiconductor devices using nitride semiconductors are used in, for example, power devices capable of operating at high frequencies and outputting high power. Particularly, FETs (Field Effect Transistors) such as HEMT (High Electron Mobility Transistor) are known as transistors suitable for amplifying in high-frequency or RF bands, which may include microwaves, quasi-millimeter waves, or millimeter waves.
The semiconductor devices using nitride semiconductors employ a protection film on a nitride semiconductor layer. It is known that the use of the silicon nitride film for protection is capable of reducing the collapse phenomenon of the drain current. It is known that the adhesion of the nitride semiconductor layer and the silicon nitride film is improved by adjusting the composition of the silicon nitride film (see Japanese Patent Application Publication No. 2006-261252, for example).
An exemplary FET using nitride semiconductors has a structure in which an insulating film covers a gate electrode having a metal pattern including Ni (nickel) provided on a nitride semiconductor layer. When voltages are applied to the FET for a regular operation, Ni contained in the metal pattern may diffuse into the insulating film, and the gate electrode may be short-circuited to another metal layer, which may cause the FET to fail.